1. Field of the Invention
The invention relates in general to a transformer and multi-lamp driving circuit using the same, and more particularly to a transformer for driving multiple lamps and balancing lamp currents simultaneously, and multi-lamp driving circuit using the same.
2. Description of the Related Art
At present, a typical liquid crystal display (LCD) has an inverter with a transformer for generating high-voltage AC signals for driving multiple lamps. In order to equalize lamp currents and thus to achieve the uniform luminance and the lengthened lifetime of each lamp, a balancing transformer for balancing the lamp currents has been adopted.
FIG. 1 (Prior Art) is a schematic diagram showing a conventional multi-lamp driving circuit 100. Referring to FIG. 1, the multi-lamp driving circuit 100 includes a driving circuit 110, a conventional transformer 120 and a balancing transformer 130. The conventional transformer 120 has a primary coil P coupled to the driving circuit 110, and a secondary coil S coupled to first ends of two coils c1 and c2 of the balancing transformer 130. In addition, the two coils c1 and c2 have the same number of windings so as to control two lamps L1 and L2, which are respectively coupled to second ends of the coils c1 and c2, to have substantially the same lamp current.
FIG. 2 (Prior Art) is a schematic diagram showing the balancing transformer 130 of FIG. 1. Referring to FIG. 2, the balancing transformer 130 further includes a core 131 and a bobbin 132 disposed in the core 131. The two coils c1 and c2 individually wind around two sides of the bobbin 132. However, the levels of the magnetic flux and the leakage inductance at each portion of the core 131 are not completely the same according to the actual pattern (e.g., the El-shape core of FIG. 2) of the core 131, and may be influenced by positions of assembled seams so that the amounts of the induced electric potential on the coils c1 and c2 are different from each other. Consequently, the balancing effects on the lamps L1 and L2 are greatly reduced. In addition, when the number of lamps is increased according to the requirement of luminance, the number of the balancing transformers 130 and the circuit complexity are also increased simultaneously so that the cost and the time for assembling the multi-lamp driving circuit 100 cannot be effectively reduced.
Although the conventional multi-lamp driving circuit may have other types of balancing transformers, this condition cannot be avoided. Thus, it is an important subject in this industry to solve the above-mentioned problems.